Very high gain traveling-wave tube



4 3 9 R Wm mz N 3 Na 2 2 me m m 2 .H H H. m 1 w? T E v A w L. BRUCK VERY HIGH GAIN TRAVELING Filed July 29, 1949 Dec. 23, 1952 Patented Dec. 23, 1952 "VERI H QLHGAINTTRAVEIJNGWAY UBE Application-Invite 9 ,'is a 1No. :9 "lnfir n egscm hcr 11,9

My inventlon relatesto ajtravelingewave'tube; its 'ob'j ect is' -to-provide a tubeiwhich has-"a ve y highwgain and in which A the possibility--of selt oscillation; is considerably reduced bya; perfect decoupling insidethetube between stheiinputtand the: output; :in particular by-- dividing: the: total gain into several stages.

The advantage of a single tube" that h-as ave y high gain .wil l be --und'erstood by consideringsthatl for a transmission dine-which is -composedof" a plurality of relays andis provided with 'travelling- Wave tubes, again :of 60 or 80 :dband' a' power of :5 or "I watt-are-required per station. "This-desired 1 gain is obtained by conne'cting incascade several stages provided with travelling-wave tubes, each ofwhich has a gaino'f ZO- or db, the :output of the ii'rst tube 'ibeing conneotedrby meansro fralguide to theinput.'o f thesecond tube, and so forth. The transfer'ofthapower "from the rtube-"to 1th= guide, and conversely,- isobtained by means. of coupling elements, the: degree "of couplingof which varies with the frequency. As a.- .result. o'f th-is, the-gain'also-varies with. the irequencyprconsequently, the'band-pass-ofrany statiorr, *which -is determined by: the: drop in the gain; 01"3 .db below the maximum value, will be narrower :asthere are: :morestagesin cascade, i. e. as there are morecouplingvelements through which the radio-drequency energy has Eto. pass.

It. is 'itherefionesdesirable to obtain asxhigh a gain::as possible from a travelling-wave :tube, so asxto obtain the tot-a1" gain required: with :a very small: number :ofsta-ges. lFor this-purpose, for example, .-it; is;v possible "to: increase .the current that :flowsethrough the helixin the :tube. -But this-.zproduces. atlessreflicient.bnnchingiioi theeljece trons/owing .to the increase in: 'the spacercharge Whiclrzreduces the expectedincrease in ithe..;gain. Furthermore, in tubes which areoons-tructedifor a high gain, there exists the-possibility o'i-a por-. tion: of the radio sirequency energ-y being reflected by the output or by a 'discontinuity ofi the-helix. If such energy reaches the input with .a power which equal to or greater thanthat of the inputsig-nal, it sets up seli osc-illation. 'I n-order toprevent this, use is made of helices which are highly attenuated for radio-irequeney energy, or of helices provided with a localized attenuation of 50 or 60- db so as todecouple the input and the outputof thehelix.

Hel-ices with an "attenuation distributed along their entire length jh-avea disadvantage, viz; that such attenuationdecreases the a n f r-a given current. -'On.-the other hand, a helix flirov lded with a localized attenuation doesnct sufliciently prevent the 'possibilitysofoscillation of'the tube, since the output energy is not transmitted'to the guidewithoutreflection, whatever the frequency may-be. 'OWing'tO this fact, andalso-becauseof the irregularities of the helix, reflections 0ccur-so that oscillations may be set up if the gain is high.

My invention enables a travelling-wave tube to be constructed, the gain of which is higher than it is possible to obtain with the tubes according to the heretofore known construction. Figs. 1 and 2 show in axial section two embodiments of the principles that enable this result to be obtained.

The invention will be explained with reference to Fig. 1. As in the tubes of usual construction, the cathode K1 emits a beam of electrons which is directed parallel to the axis of the helix H1. The radio-frequency signal is intrcduced into the helixzin the known manner by means of members not-shown. The helix-is manufactured or a material that has a low radio-frequency attenuation, so that the losses of radio-frequency energy in the-helixa-re small. In order only to have waves which are propagated in the direction of the electrons along the helix, the end of said helixon the output side is in contact with a layer R1 of resistance material arranged on the quartz rods T1 or on the wire of the helix, said layer being matched at its input with the characteristic impedance of the helix, thereby preventing a reflec-tion of the radio-frequency energy. After the electrons have passed through the helix H1. they are collected. by the collector C1. The device comprisingthe cathode K1, the helix Hipand the collector C1 therefore difiers from the .lgnown travelling-wave tubes only by the fact thatthe outputzend oftheihelix is matched for all frequen-v cies and does not produce any reflection of the radio-.f'reguency energy. This already considerably lessens the probability of self-oscillation. Furthermore, in orderto reduce thev possibility of a self-oscillationof the tube caused by irregularities on the helix, the helix H1 may be provided with a localized attenuation A, in a manner known per se.

A tube which has the above characteristics and which corresponds'to this first portion of the tube of Fig. '1 already enables a higher gain to be obtained than it is possible to obtain in tubes provided with a localized attenuation according to thezknown construction. A subsequent improvement can however be obtained by-applying other arrangements according to fthe invention, which are shown in'Eie L The radio-frequency energy of the first travelling-Wave tube K1H1C1 controls the electrons of a second beam F2 which is emitted by a cathode K2 located outside the helix H1 at an intermediate point of same. This beam propagates outside the helix H1 and interacts with a second helix H2 which is located outside the beam F2, for example in the axis of the helix H1, and which is of the same diameter as said helix Hi. In this manner, the electrons of the second beam F2 are velocity-modulated along the last portion of the helix H1, after which the modulated beam produces in the helix H2 a radio-frequency wave that propagates towards the output. The electrons of the beam F2 are collected by a collector 02, while the radio-frequency energy is collected at the output in the known manner, for example by coupling the output to a guide not shown. The helix H2 is provided at its input end with a layer R2 of resistance material arranged on the quartz rods T2 or on the wire, said layer producing sufficient attenuation for the radio-frequency energy which is being propagated from the output towards the input end to be completely absorbed at the input end of the helix H2.

The cathode K2, which is shown in section in Fig. 1, may be of annular shape which is only broken if necessary by the rod or rods T1. In this case, the beam F2 substantially completely surrounds the helix H2 and consequently, for a given cathode current, has a smaller space charge than in the case in which the beam is located inside the helix. Thus, the unfavorable eiiect of the space charge on the gain remains slight.

The focusing of the two beams in the direction of the helices is obtained by means of a ma netic field along the axis of the tube, in the manner which is known in the tubes of usual construction.

With a tube according to Fig. 1, there is not only the advantage of being able to obtain a higher gain than in the known designs, but there is furthermore the possibility of obtaining the necessary absolute radio-frequency power which is required at the output of a station, such power being determined by the current of the cathode K2 and by the accelerating voltage of the beam F2.

Fig. 2 shows a modified embodiment of the principles of the invention. The elements which are similar to those of Fig. 1 have been designated by the same reference letters. The difference with respect to Fig. 1 is that the helices are housed in a metal casing M which, together with the helix H2, determines a radial field which is used to control the beam F2. The cathode K2 is again annular but the helix H2 is no longer located inside but outside the beam F2. The collectors C1 and C2 can thus be combined into one member, thereby facilitating the supplying and cooling of the collector C1.

My invention is not restricted to the examples which have been described and illustrated, but on the contrary can be subjected to any modifications that an expert might be able to make therein without altering its principle.

What I claim is:

1. A travelling-wave tube comprising inside a single casing a chain of systems, each of which comprises 2. source of an electron beam, a collector positioned at the extremity of the path of the beam for collecting the electrons of the beam, and a retardation line extending parallel to the path of said beam, the output of a retardation line of a first system, which has a beam passing inside.

4 said line, being coupled to the beam of a second system, that passes outside said line, the beam of said second system being in turn coupled to the retardation line of said second system in a subsequent portion of the tube.

2. A travelling-wave tube comprising inside a single'casing' a, chain of systems, each of which comprises a source of an electron beam, a collector positioned at the extremity of the path of the beam for collecting the electrons of the beam, and a retardation line extending parallel to the path of said beam, the output of a retardation line of a first system, which has a beam passing inside said line, being coupled to the beam of a second-system, that passes outside said line, the beam of said second system being in turn coupled to the retardation line of said second system in a subsequent portion of the tube, said second beam being located outside the said corresponding retardation line.

3. A travelling-wave tube comprising inside a single casing a chain of systems, eachof which comprises a source of an electron beam, a collector positioned at theextremity of the path of the beam for collecting the electrons of the beam, and a retardation line extending parallel to the path of said beam, the output of a retardation line of a first system, which has a beam passing inside said line, being coupled to the beam of a second system, that passes outside said line, the beam of said second system being in turn coupled to the retardation line of said second system in a subsequent portion of the tube, this second retardation line being located outside the said corresponding beam.

4. A travelling-wave tube comprising inside a single casing a chain of systems, each of which comprises a source of an electron beam, a collector positioned at the extremity of the path of the beam for collecting the electrons of the beam, and a retardation line extending parallel to the path of said beam, the output of a retardation line of a first system, which has a beam passing inside said line, being coupled to the tubular-shaped beam of a second system, that passes outside said line, said tubular-shaped beam being in turn coupled to the retardation line of said second system in a subsequent portion of the tube.

5. Travelling-wave tubes comprising inside a single casing a chain of systems, each of which comprises a source of an electron beam, a collector positioned at the extremity of the path of the beam for collecting the electrons of the beam, and a retardation line extending parallel to the path of said beam, the output ofa retardation line of a first system, which has a' beam passing inside said line; being coupled to the beam of a second system, that passes outside said line, the beam of said second system being in turn coupled to the retardation line'of said second system in a subsequent portion of the tube, said second retardation line being located outside the said corresponding beam, and the collectors of the successive systems being combined in a single member. 6. Travelling-wave tubes comprising inside a single metal casing a chain of systems, each of which comprises, means for producing and accelerating an=electron beam, a collector positioned at the extremity of the path of the beam for collecting the electrons of the beam, and a retardation line extending parallel to the path of said beam, the output of a retardation line of a first system, which has a beam passing inside said line, being coupled to the beam of a second system, that passes outside said line, the beam of said 5 second system being in turn coupled to the retardation line of said second system in a subsequent portion of the tube, the retardation line of said second system being located outside the said corresponding beam.

LOTHAR BRUCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,541,843 Tiley Feb. 13, 1951 2,578,434 Lindenblad Dec. 11, 1951 OTHER REFERENCES Article by Andrew V. Haefi, pp. 47, inc1., Proceedings of the I. R. E., January 1949.

Article by A. V. Hollenberg, pp. 52-58, incL, Bell System Tech. Jour., v01 1, No. 1, January 1949. 

